The present invention is directed to a method for recovery of the energy values of oily refinery sludges, in general, and to a method for the use of such materials as a fuel source in a rotary mineral processing kiln, such as a lime, light-weight aggregate, asphalt or cement kiln, in particular.
Oily refinery sludges are generally described as oily solids consisting primarily of finely divided particles (which may or may not exhibit suspension characteristics) contained in or removed from aqueous streams. In addition to oil and water, such sludges often comprise sediments such as sand and silt that accompany the crude oils into the refinery, other materials such as heavy metals and organics, and corrosion/erosion products that result from refinery operations. Prior to dewatering, such sludges typically contain about 40 to 90 percent water by weight.
Petroleum refineries have a number of sources of oily refinery sludges. For instance, water which may be contaminated with oil is typically diverted to large concrete sumps called API separators where an oily sludge is separated from the water. The clarified water from the API separators may then be further purified by coagulation of impurities in floatation tanks, such as dissolved air floatation tanks, with the impurities being removed as an oily sludge. Other sources for oily refinery sludges include heat exchanger bundles, slop oil emulsion solids and tank bottoms.
Until recently, such sludges have been sent to a settling lagoon for dewatering. No further treatment was required nor typically performed. However, recent environmental concerns have created a need for further treatment of such materials.
The primary treatment method currently being proposed is incineration to destroy the organics or solvent extraction of the sludge to remove the hazardous organics followed by landfilling. However, the energy content of the material is not recovered in this method and the associated costs are somewhat prohibitive.